Digital Radiography (DR) systems are being employed in medicine and industry, with particular value as clinical imaging tools. As shown in the simplified block diagram of FIG. 1 of a prior art system, radiation from a radiation source 12 in a DR imaging apparatus 10 is directed through a subject 14 and impinges on a radiation detector 30 that includes a scintillator screen 16 for converting the energy from ionized radiation into light radiation having a different frequency, typically within the visible spectrum, and an image sensing array 20. Image sensing array 20, typically mounted on the backplane of scintillator screen 16 or otherwise optically coupled with scintillator screen 16, forms a digital image from the emitted light that is excited by the incident radiation. The digital image thus formed can be processed and displayed by an image processing apparatus on a control logic processor 18, typically provided by a computer workstation and display 19.
Unlike conventional x-ray film apparatus, DR imaging apparatus 10 does not require a separate processing area, light-protected environment, or image processing consumables. An advantage of DR imaging technology is speed, since images are obtained substantially immediately after the x-ray exposure. As such, for medical applications, a diagnostic image can be provided to medical personnel while a patient is still present at an imaging facility.
In conventional x-ray film applications, there has been a continuing need for projection x-ray film media of sufficient size to image larger body parts. Body parts having a high length-to-width aspect ratio (e.g., the spine or a full leg) are film imaged using a technique called long length imaging (LLI). Observations and measurements from those films are useful for many conditions, such as in diagnosing scoliosis, where the Cobb Angle is measured, or measurements of leg length, angulation and deformity are obtained. To meet the demand for long length imaging, existing film screen cassette sizes up to 35 cm×130 cm can be used.
FIG. 2 shows a prior art conventional film imaging embodiment wherein both an x-ray tube 101 and a film cassette 103 are stationarily maintained during a long length imaging exam. The beam from x-ray tube 101 can be collimated to a desired x-ray coverage exposure area 102. An image of a patient 100 can then be acquired in a single exposure.
As FIG. 2 shows, film is advantaged for long length imaging since it can be provided in a large sheet when needed. In contrast, digital projection radiography, provided by both Computed Radiography (CR) and Digital Radiography (DR) systems, uses a fixed-size image detector. This makes long length imaging more difficult for both CR and DR systems. For example, flat panel DR plates are generally available in a small number of sizes, up to a maximum extent of about 43×43 cm. A detector of this size can image only a portion of the body part at a time and so is inadequate for performing imaging exams of longer length body parts such as the full spinal column or full leg.
Some CR apparatus address long length imaging. For example, Eastman Kodak Company provides stitching software and a cassette positioning system for LLI that delivers images up to 17 inches wide by 51 inches long (43×129 cm). This can be obtained using a single CR cassette or using multiple CR cassettes. However, CR cassettes require scanning apparatus in order to read the exposed image. So, while there is no longer a film processing step when using CR cassettes, there remains a scanning step and a process for erasure with CR cassette processing. The handling and identifying of the unprocessed cassette data that is not yet scanned creates workflow and data collection issues at some sites. Some CR long length imaging apparatus are described in U.S. Pat. No. 6,744,062 (Brahm), U.S. Pat. No. 6,895,106 (Wang), and U.S. Pat. No. 6,273,606 (Dewaele).
DR systems with flat-panel detectors offer some advantages over film-based and CR cassette systems with respect to workflow. However, the cost and technology constraints of DR panels limit detector size and complicate the task of long length imaging.
There have been some proposed long length imaging with DR systems. In general, these systems obtain a sequence of multiple exposures/images at varying positions, with the assumption that the patient remains still during the exam. The individual images are then stitched together to reconstruct a larger composite image.
FIG. 3 shows an exemplary technique, using tube and detector translation, for example as described in U.S. Pat. No. 5,123,056 entitled “WHOLE-LEG X-RAY IMAGE PROCESSING AND DISPLAY TECHNIQUES” to Wilson and U.S. Pat. No. 4,613,983 entitled “METHOD FOR PROCESSING X-RAY IMAGES” to Yedid et al. With this technique, the detector or the patient or both are translated along a path that allows collection of a sequence of partial images to be obtained. The final image of a longer length body part that exceeds the image acquisition area of the detector can be obtained from a composite of the individual partial images. As shown in FIG. 3, a patient 200 is exposed as defined by an x-ray tube first position 201 and a detector first position 203. A collimator of the x-ray tube is adjusted by the technologist such that an x-ray exposure area 202 can covers the detector while protecting the patient from unnecessary radiation in the non-imaging related regions. Subsequently, both the x-ray tube and the detector are translated in parallel along a tube axis of motion 210 and a detector axis of motion 211, respectively, to a second position, as indicated by an x-ray tube second position 206 and a detector second position 208. A second exposure of the patient is taken with the x-ray tube and detector in their second position, with x-ray exposure area 207 covering the detector. There may be an overlap between coverage areas for consecutive detector positions, in order to facilitate image stitching. This process for obtaining partial images is continued until the full length of the body part to be examined has been imaged.
While the sequence described with reference to FIG. 3 can allow a larger image to be formed from separate smaller images, there are some disadvantages. For example, an apparatus providing movement of both the detector and the x-ray tube can be mechanically complex. Some amount of geometric distortion is inherent with such an arrangement, which can make it difficult to obtain precise image stitching. The severity of the image-stitching problem can increase with increasing thickness of the body part.
FIGS. 4A and 4B show another method for field translation based on x-ray tube angular rotation, such as that described in commonly assigned U.S. Patent Application Publication No. 2002/0159564 entitled “METHOD FOR ACQUIRING A RADIATION IMAGE OF A LONG BODY PART USING DIRECT DIGITAL X-RAY DETECTORS” by Wang et al. Using a detector 303 positioned at first position 307, a patient 300 is exposed to x-rays 302 from and x-ray tube 301 having an axis of rotation about a point 3 10. X-ray tube 301 is directed toward detector 303. Detector 303 is translated along a detector axis of motion 311 between each exposure, while x-ray tube 301 is rotated about point 310 between each exposure. For example, with detector 303 positioned at second position 308, the x-ray tube (shown in FIG. 4B as x-ray tube 304) is rotated about point 310, and patient 300 is exposed to x-rays 305. Following image acquisition, the individual images are stitched together as if the whole image had been acquired with a single x-ray exposure using the film geometry of FIG. 2.
FIGS. 5A and 5B show another method for field translation using a collimation shutter 404 mounted adjacent an x-ray tube 401, as described in commonly assigned U.S. Patent Application No. 2002/0191750 entitled “COLLIMATION DEVICE AND METHOD FOR ACQUIRING A RADIATION IMAGE OF A LONG BODY PART USING DIRECT DIGITAL X-RAY DETECTORS,” by Wang et al. A focal point 410 is provided for exposing a patient 400 and capturing the image using detector 403. The x-ray tube remains stationary, and collimator shutter 404 translates to an appropriate position to redirect the emitted x-rays. Detector 403 translates along an axis 411 to receive the x-rays. Collimation shutter 404 has a particular size opening, and moves adjacent x-ray tube 401 to selectively expose the portion of the patient adjacent the detector. For example, at a first position 407 receiving a first x-ray exposure 402, and then at a second position 408, receiving a second x-ray exposure 405.
The individual images can be “stitched together” (i.e., combined) to form a full size image of a long length body part. For example, U.S. Pat. No. 6,944,265 entitled “IMAGE PASTING USING GEOMETRY MEASUREMENT AND A FLAT-PANEL DETECTOR” to Warp et al. describes a process for forming a composite image from individual image segments. U.S. Pat. No. 6,895,076 entitled “METHODS AND APPARATUS FOR MULTIPLE IMAGE ACQUISITION ON A DIGITAL DETECTOR” to Halsmer et al. describes a system for long length imaging that includes operator identification of top and bottom (start and stop) positions, calculations for overlap between successive images, an imaging operation controller that controls x-ray source operation, and a position changing apparatus for changing the relative position of the x-ray source and the subject of interest.
Matching the capabilities of conventional film-based systems for long length imaging continues to pose a challenge to DR system design and operation. For example, obtaining a long length image with conventional DR systems remains operator intensive. The operator monitors and controls each movement or set of movements that adjust the position of the x-ray source and detector mechanisms. Exposure settings for each individual image require operator attention. Even though images may be stitched together with some degree of automation, there remain considerable demands on operator time and attention for long length DR imaging. There exists a need for a system providing seamless integration of operator control, user interface, software function, and hardware movement. Such a system would mimic the operator workflow used in screen-film systems.